Filters and Fog
I've read on both Ilford's webpage and other places that a blue filter will enhance fog and haze. Does anyone have side by side image examples of the increase? I've been trying to get out whenever there is heavy fog and I have been primarily using either no filter or a polarizer -
This is a common advertising pitch that is quite a bit oversimplified.
Originally Posted by mporter012
Much distance haze and mist/fog is made up of water vapor and pollutants that absorb a lot of the red and green light striking/passing through it and reflects/passes mostly blue. This means that IF there are objects in the scene that are illuminated by another light source (say, the sun) and you use a blue filter, the haze/mist/fog that is mostly blue will be rendered lighter than "normal" (i.e., what you see).
If, however, the entire scene is foggy, and the only illumination you have is being filtered through the fog (such as on a foggy day on the coast while you're on the beach), then there is no difference in color to be had; everything is relatively bluer compared to daylight (much like shooting in open shade) and your blue filter will simply affect overall exposure less predictably (i.e., your filter factor will be different than for daylight). This will likely result in a slight overexposure if you apply the daylight factor, but will NOT render the fog much lighter relative to other neutral subjects (which are all illuminated by the same color light).
So, use the blue filter to lighten and "enhance" distance haze and mist/fog in scenes that have other general illumination sources (say, a scene of rolling hills with mist and haze in the distance). The approximate opposite of this is using a yellow filter to reduce the effect of distance haze in landscapes.
However, when photographing in the fog itself where there is only light filtered by the fog, your blue filter will have little effect on contrast. It is better to deal with this delicate rendering by controlling contrast using standard exposure/development controls guided by careful visualization of how you want to render the fog (this is a bit tricky for many).
Hope this helps,
It is the red light that passes more through haze than blue light.
Originally Posted by Doremus Scudder
That means if on a very hazy day you want to "cover" something in that haze, or with other words to emphasize on that haze, a blue filter would do so.
Nonwithstanding whether the light source is within or outside the haze.
In colour photography the resulting blue effect could be filterd out in a later stage.
Last edited by AgX; 01-22-2013 at 05:29 AM. Click to view previous post history.
Thanks for the great info!
Originally Posted by AgX
Sorry, I beg to differ.
Water vapor and most particulates and pollutants absorb or scatter the longer wavelengths and pass the shorter (blue end of the spectrum) (this is what makes the sky blue, not red...).
Anyone who has been more than a few meters underwater (snorkeling or scuba diving) knows that everything turns blue; the longer wavelengths (red, yellow, green) get filtered out because they are absorbed; the blue passes through. The same thing happens with water vapor in the air. Cloudy days are markedly more blue than sunlit days for precisely this reason; the longer wavelengths are filtered out by the clouds.
UV or yellow filters are sometimes called "haze filters." They "eliminate" the haze by darkening it, i.e., by blocking the predominantly blue (and near UV) shorter wavelengths making the haze darker and less noticeable in the print. Using a blue filter passes those shorter wavelengths and makes the haze lighter, thereby "emphasizing" it.
A clear UV or haze filter is what is generally used in color photography to "eliminate" or "reduce" haze, which it does by blocking the near UV and a bit of the darkest blue. These are the wavelengths that are predominant in haze.
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Actually the blue is more strongly scattered.
"There are a great many things I am in doubt about at the moment, and I should consider myself favoured if you would kindly enlighten me. Signed, Doubtful, off to Canada." (BJP 1914).
Haze: Page 102, The Negative (Adams). Reading this book for as many times as it takes to sink in will likely do more for your inquiries here than the good intentions of most posters (in deference to Doremus' considerable contributions).
Originally Posted by mporter012
Fog: I defer to anything written in The Negative or Natural Light Photography (#4 in the Series, Adams), but I use yellow to increase contrast of elements in the scene only if that is what I've visualized. Normally the point of shooting in fog is, well, the fog.
Last edited by ROL; 01-23-2013 at 11:59 AM. Click to view previous post history.
Thanks ROL. I'm reading The Negative now. I was unaware of Natural Light Photography. Good to know man.
Have you ever used filters?!
Originally Posted by Doremus Scudder
It's not a matter of transmitting or absorbing. It is a matter of scattering the light. The sky is blue simple because whatever is in the sky scatters blue rays more.
Go up on an elevated area such as a really tall building or a mountain and then take a landscape picture with some fine grain film with a deep red filter (3 stops of compensation). Then take the same picture without the filter. You will be able to see a lot more detail with the red filter. Once you filter out the scattered blue light you will get the more direct red light. Now take the picture with the blue filter. Details will be obscured.
I read about red filters cutting through haze but I didn't realize how dramatic the effect was until I tried it for myself. I took the pictures on a clear bright day and you could still see a difference. Try it with a red filter AND a polarizer. It's even more dramatic. Bring a tripod and cable release.
The benefits of a red filter particularly a strong red filter cannot be duplicated with a digital camera or photoshop. It really is one of the unique tools of analog photography.
Gee, I think I might have used a filter a time or two in my 30+ years of photography... I also studied physics of light and optics as an adjunct to my other university studies. I think I have a fairly good understanding of what filters do.
Originally Posted by Noble
Anyway, all flippancy aside, I think we are saying fundamentally the same thing; I just think you have missed the gist of the OP's original post.
And yes, the blue sky is from scattered blue light, but in a transmission spectrum of water or clouds or fog, you will find that the longer wavelengths are absorbed more, resulting in a higher color temperature (i.e., more blue).
The original question was about "enhancing" fog, not "eliminating" it. I agree, that a yellow or red filter will do exactly what you say it will. And, a blue filter would do just about the opposite, i.e., lightening and "enhancing" the haze; that is, making it more apparent.
Note that there is a fundamental difference between shooting a scene with haze in it that is otherwise lit with "normal" sunlight and shooting from within the fog (which is what I believe the OP was addressing). Use of a blue filter in this case will just overexpose the film a bit, since the factor for the filter is not based on the color temperature of the light coming through the fog. It will no appreciably enhance the foggy effect.
Hope this clears things up,